The aim of this research study is to identify unusual body rhythms in totally blind people that are associated with insomnia and impaired daytime alertness, and to synchronize these rhythms to a normal 24 hour cycle with daily melatonin administration. It has recently been determined that environmental light is an important factor in synchronizing internal 24-hour ("circadian") body rhythms, and that some blind people may not synchronize their rhythms because of the absence of visual perception. If circadian rhythms are consistently greater than 24-hours, they are termed "free-running rhythms." These unusual body rhythms might result in periodic sleepiness or insomnia. A goal of the study is to determine if giving melatonin (either a 0.5 mg or a 10 mg dose) by mouth before bedtime will change the rhythm of the internal body clock, and normally synchronize it to a 24-hour cycle. Also, melatonin may have some sleep-promoting (sedating) effects that could enhance nighttime sleep. Melatonin is a hormone made by the pineal gland in the brain and is normally secreted at night. Melatonin is currently considered an experimental drug. Previous research by our group indicates that treatment with melatonin may be able to enhance the rate at which the body can shift to a new sleep schedule, which may in turn help alleviate problems with insomnia. We hope to develop melatonin as a way to treat blind people with free-running rhythms. There are two secondary purposes within this study. The first is to investigate the manner in which blind people process auditory information. This involves a series of auditory perception and memory tasks and requires about 90 minutes to complete. We are also attempting to link free-running rhythms to a genetic marker. Participants may choose not to participate in either the auditory testing or the genetic portion of this protocol and still be a part of the overall study.